1. Field of the Invention
The present invention relates generally to the field of parametric loudspeakers and signal processing systems for use in audio reproduction. More particularly, the present invention relates to parametric emitters formed of substantially rigid plates or generally planate emitter structures.
2. Related Art
Non-linear transduction, such as a parametric array in air, results from the introduction of sufficiently intense, audio modulated ultrasonic signals into an air column. Self demodulation, or down-conversion, occurs along the air column resulting in the production of an audible acoustic signal. This process occurs because of the known physical principle that when two sufficiently intense sound waves with different frequencies are radiated simultaneously in the same medium, a modulated waveform including the sum and difference of the two frequencies is produced by the non-linear (parametric) interaction of the two sound waves. When the two original sound waves are ultrasonic waves and the difference between them is selected to be an audio frequency, an audible sound can be generated by the parametric interaction. Emitters suitable for producing such an effect are referred to herein as “parametric emitters.”
While the theory of non-linear transduction has been addressed in numerous publications, commercial attempts to capitalize on this intriguing phenomenon have largely failed. Most of the basic concepts integral to such technology, while relatively easy to implement and demonstrate in laboratory conditions, do not lend themselves to applications where relatively high volume outputs are necessary. As the technologies characteristic of the prior art have been applied to commercial or industrial applications requiring high (or even useful) volume levels, distortion of the parametrically produced sound output has resulted in inadequate systems.
Whether the emitter is a piezoelectric emitter or PVDF film, in order to achieve volume levels of useful magnitude, conventional systems often require that the emitter be driven at intense levels. These intense levels have been often greater than the physical limitations of the emitter device, resulting in high levels of distortion or high rates of emitter failure, or both, and without achieving the magnitude required for many commercial applications.